Research focuses on water use efficiency

Declining water tables and rising energy costs have forced many West Texas farmers to consider ways to improve irrigation efficiency.

That’s why Texas A&M research agricultural engineer Jim Bordovsky devotes much of his efforts at the Helms Research Farm in Halfway, Texas, to discovering ways to apply irrigation water more efficiently. Bordovsky discussed some of his research recently at a Helms Farm field day.

“We’re looking at heat units as well as soil moisture levels to schedule irrigation,” Bordovsky told field day participants. “Scheduling this year has been difficult because we had more rainfall than normal and are using several unfamiliar cotton varieties. “Ironically, rainfall makes determining when to irrigate more challenging. We have to try to determine how much rain infiltrates into the soil profile and contributes to plant development.”

He said some of the cotton in his trials developed rank growth this year. “We irrigated some fields a lot and some a lot less.” He said heat unit evaluation offers researchers and ultimately growers a tool to evaluate plant development and irrigation needs. He also considers evapotranspiration rates determined from a nearby weather station to calculate moisture losses.

He’s also looking at subsurface drip irrigation systems to determine “how best to save water and irrigate economically with this system. The question has been whether to concentrate water (and other) resources or to spread them out over a larger area. Conventional wisdom in the past has been to spread available water over a larger acreage, especially with center pivot units.”

Apparently the thinking was that the pivot units represented significant investments that should be used on all the acreage systems covered each growing season. Bordovsky is evaluating drip irrigation to determine how concentrating water on smaller areas and enhancing management affects production compared to more normal methods. He applies fertilizer through the system, lowers the pest insect threshold, plants a less determinant cotton variety and uses plant growth regulators aggressively.

“We compare highly managed acreage with less intense management,” he said. High management plots were irrigated to insure no moisture stress, resulting in applications of more than 15 inches of water through the growing season. The normal managed areas were irrigated at a maximum rate of 0.2 inches per day, reaching a total of 11 inches. “For the past two years the high management plots netted a 400 pound per acre yield advantage,” Bordovsky said. “That’s an average over two years.”

That production increase also meant a $200 per acre added value to the cotton crop. “Those two years were both dry,” Bordovsky said. “This growing season has been completely different and it will be interesting to see how the plots compare after harvest.”

John Gannaway, cotton breeder with the Texas Agricultural Experiment Station in Lubbock, cooperates with Bordovsky to compare varieties under different drip management practices. He selects 24 varieties and evaluates them under dry as well as normal and high input management regimes.

“We want to determine the effect of variety on yield under various moisture and management conditions,” he said. “This is the third year we’ve run the small plot variety trials with the same varieties each year. “So far, we’ve identified individual varieties that yield well in one or two of the three management regimes and a few varieties that have worked well under all moisture and management conditions.”

Bordovsky said drip irrigation typically is associated with high value crops where uniform water distribution is critical. “We’re testing drip uniformity designs in cotton to determine if traditional design standards can be relaxed without hurting total yield. “We’re using three designs with different drip tape diameters and pressures to achieve poor, adequate and very good water distribution uniformities in replicated test plots.”

Half of the test plots were irrigated at levels to meet crop moisture demand, the other half irrigated to meet 60 percent of demand. He said he got good data from the test in 2001 but had some emitter plugging and weather damage problems the last two years. “Results have been somewhat consistent nonetheless,” he said. “With 60 percent demand, the poor design resulted in high yields where more water was applied in the plot and lower yields in areas of lower water application. However, total yield within the plot matched that of the very uniform drip design. A similar trend occurred in areas irrigated at 100 percent demand. That may mean we can relax our standards somewhat and get drip irrigation systems that are a bit less expensive to install.”

He said the test may help determine a level of uniformity farmers can tolerate if water tables fall and they have less water to apply. He cautioned that water distribution may affect cotton seed germination, however.

Plant pathologist Terry Wheeler is using soil electrical conductivity to determine “where the best soils in a field are located and evaluate yields in high and low production areas.” She said the study is designed to determine if growers can change how they distribute water. “Can we redistribute water and improve overall production? That’s the question,” Wheeler said. “So far, we’ve found no benefit. But we have found a correlation between soil electrical conductivity and yield.”

She said the study also uses remote sensing to evaluate effects of tillage, nematodes and nitrogen rates. “We try to identify stress in plants and determine what causes it in each field,” she said.